Plastic bottles are widely used as containers for retailing soft drinks and other beverages. One type of plastic, polyethylene terephthalate (PET), has become particularly popular because of its transparency, light weight, and low cost. In addition to being flexible, the walls of PET bottles are strong in tension and thus can safely contain the pressure of a carbonated beverage. Moreover, conventional PET bottles can bear surprisingly high compressive loads, provided that the load is directed substantially along an axially symmetric axis of the bottle. A single PET bottle can support the weight of many bottles of the same size filled with beverage if the bottle is standing upright on a flat, horizontal surface and the weight of the other bottles is applied to the closure of the single bottle and is directed substantially vertically along the symmetric axis. However, if a compressive load is applied to a conventional PET beverage bottle along a direction other than the symmetry axis of the bottle, the bottle tends to buckle. This tendency of conventional PET bottles to give way under off-axis compressive loads is particularly pronounced for large capacity bottles, such as the two-liter bottle widely used for marketing soft drinks.
Soft drink bottles are ordinarily packaged by bottlers in cases or other containers, several bottles to the case, for shipment to retailers or for storage. Cases of bottles are customarily stacked on top of each other. In warehouses, cases of bottles are frequently stacked on pallets which can be lifted and moved about by fork-lift trucks. The stacks of cases on the pallets must therefore be particularly stable in order to remain standing in the face of the jostling inherent in being moved about. A technique for interconnecting columns of cases, called "cross stacking," is often used to improve the stability of cases of bottles loaded on a warehouse pallet. Cross stacking generally involves stacking rectangular bottle cases to build up a layered structure, with each layer having cases oriented parallel to each other and with the cases in adjacent layers being oriented at right angles to each other. Since each case in the cross-stacked layer rests on at least two cases in the layer below, the cases of the cross-stacked layer tend to keep the cases on which they rest from moving apart from each other. The cross-stacked layer therefore stabilizes the structure.
Because of the tendency of conventional PET beverage bottles to buckle under off-axis loads, attempts to stack cases of these bottles give rise to serious problems. Bottles can tilt away from vertical alignment upon stacking if conventional partitioned cases having low side walls are used to contain the bottles. Tilted bottles in the lower cases of a stack can buckle and give way, causing the stack to fall. Even absent buckling, the tendency of bottles to tilt in conventional low-sided cases causes problems. Tilting generally places an undesirably low limit on the number of tiers in a stack since the tilting of bottles in one case can cause the next higher case in the stack to tilt. This leads to instability if too many tiers are included in the stack.
Previously, these problems were dealt with by packaging beverage bottles in corrugated-paper cartons having high sides, often equal in height to the height of the bottles. Two-liter PET bottles filled with soft drinks were often packaged in enclosed corrugated paper cartons for storage and shipment. Although the high sides of these paper cartons reduce the incidence of tilting and provide additional support when the cartons are stacked, the cartons are expensive. The cost of the cartons cannot ordinarily be distributed over a number of repeated uses since corrugated-paper cartons generally are not rugged enough for reuse and therefore they are usually discarded by the retailer.
One solution to the problems of full depth corrugated-paper cartons is plastic full depth cases. In plastic full depth cases, the sides are load bearing. Full depth plastic cases also have numerous disadvantages. They are expensive to manufacture. They are also expensive to ship and to store empty in a user's warehouse as they require lots of space. Also, they totally surround the bottles, thereby preventing display of the bottles.
To overcome these problems plastic low depth cases have been used. A low depth case is one in which the side walls are lower than the height of the stored bottles, and in which the bottles support the weight of additional cases stacked on top. Some examples of low depth cases follow. However, these too have drawbacks. Some cases, such as the cases disclosed in the deLarosiere, require additional structure to hold the bottles and insure complete bottle stability, even though the case depth is more than 25% of the height of the bottles.
Various plastic reusable bottle carriers are known in the art. One reusable bottle carrier is disclosed in U.S. Pat. No. 3,055,542 to Russo. The bottle carrier can be made of a plastic, and is assembled from two pieces: a handle and a carrier body having six cups for soft-drink bottles. In order to stack the bottle carriers when empty, the handles must be removed. This is very inconvenient and time consuming. The '542 bottle carrier is also seriously limited regarding stacking loaded carriers. It cannot be stacked in a conventional cross-stacked structure because, as shown in FIGS. 3 and 10, the spacing between the bottles in the carriers is different in the directions parallel and perpendicular to the handle of the carrier.
Kappel U.S. Pat. No. 2,970,715 is one of the earlier embodiments of molded plastic low depth bottle carrying cases. Each bottle rests on a raised flat surface within an individual compartment. The bottom of the case is formed with recesses for receiving bottle tops when loaded cases are vertically stacked. However, Kappel does not indicate the size of the carrying case relative the bottles being carried.
In Bunnell, U.S. Pat. No. 3,812,996, a reusable plastic bottle carrying case for beer bottles is disclosed. The case is designed with a plurality of bottle compartments having flat bottom walls. The cases are designed to be cross-stacked; the cases are dimensioned so that the center-to-center distance between adjacent bottles within a case is the same as the center-to-center distance between adjacent bottles in adjacent cases in abutting relationship. The bottles are co-linear. Although a plurality of loaded carrying cases is designed to be vertically stackable with the weight of upper cases supported by the bottles within lower cases, the outer surface of the bottom wall of the case is flat.
Garcia, U.S. Pat. No. 3,247,996 discloses a low depth plastic bottle container for milk bottles. The container is shorter than the bottles which extend above the top surface of the container walls. In Garcia, the bottles, rather than the walls of the container, are load bearing. Indented circular portions may be formed in the bottom wall to receive bottle tops when containers are vertically stacked. Like many prior art bottle carriers, the Garcia container is a low depth case that can be used with a variety of bottles. However, the case is not a very low depth case and is more expensive than very low depth cases. It also does not have the display capabilities of very low depth cases.
A more recent attempt to solve the problem of providing reusable, cross-stackable PET bottle cases is disclosed in U.S. Pat. No. 4,344,530 to deLarosiere. The '530 patent has many of the features and problems of Garcia and discloses a plastic PET bottle case that is cross stackable and has a very low depth as shown in the figures. This low depth is disclosed as being approximately 1/6 the height of the PET bottles, or approximately 2 inches. However, in practice, this depth is insufficient and does not prevent bottles from tipping over. This creates a large degree of lateral instability. In practice these cases are 3-331/4 inches high. Additionally, the bottle retaining pockets are required to have a raised annular bottle seat ring which fits within the inner indentation formed in the base of many bottles to insure bottle stability. Also, this does not permit petaloid bottles to rotate within the bottle pockets for display purposes. Additionally, it does not permit bottles without a base indentation to be adequately retained. deLarosiere also incorporates a bottle spacing feature that co-linearly aligns bottles to facilitate cross stacking.